1. Field of the Invention
The present invention relates to a slider for a slide fastener.
2. Prior Art
A known slide fastener comprises a pair of fastener stringers including a pair of stringer tapes carrying along their longitudinal edges a pair of rows of fastener elements; each row of the fastener elements is in the form of a coiled plastic filament attached by sewn stitches to the respective tape on one face thereof. Each of such fastener elements has a substantially oval contour and hence tends to roll or tilt in a slider when a lateral pull is exerted on the tape. This rolling causes not only unstable coupling of the opposed rows of fastener elements but also non-smooth movement of the slider.
In an attempt to solve this problem, as shown in Yunnaga U.S. Pat. No. 4,419,705 filed June 2, 1981, an improved slider has been proposed in which a pair or corner ledges is disposed on an upper wing adjacent to a pair of lateral flanges respectively, each corner ledge extending along an inner face of the respective flange throughout its length. Each corner ledge has an inwardly sloping surface engageable with leg portions of the respective row of fastener elements which leg portions are disposed remotely from the tape and face the flanged upper wing. However, the prior slider cannot prevent rolling of the fastener elements, in case it is used in a slide fastener in which a pair of rows of coiled filamentary fastener elements is disposed on the underside of the respective stringer tapes. Furthermore, if the flange and corner structure of Yunnaga were modified to be disposed on the lower flange to accommodate fastener elements on the underside of the tapes, the result would still be unsatisfactory. In such particular modified slide fastener, as shown in FIG. 1 of the accompanying drawings, both the lateral flanges 6 (only one shown for clarity) and the corner ledges 7 (only one shown for clarity) are disposed on the lower wing 2 of the slider body, and the upper wing 1 has an aperture 1a through which a fastener-element locking pawl of the slider is projectable in response to pivotal movement of a slider pull tab pivotally mounted on the upper wing 1. When a lateral pull in the direction of an arrow 8 is exerted on one tape 3 while the opposed rows of fastener elements 4 attached to the respective tapes 3 by sewn stitches 5 are being coupled to close the slide fastener, the individual fastener elements 4 on the one tape 3 tend to roll or tilt in the guide channel of the slider. At that time, the outer or lower leg portion 4b of the fastener element 4, as the latter arrives at the aperture 1a, falls on the inner face 2a of the lower wing 2 so that the coupling head portion 4a partly projects into the aperture 1a, thus causing not only non-smooth movement of the slider but also non-uniform spaces between the fastener elements 4.